A conventional frequency selective surface comprises a doubly periodic array of identical conducting elements, or apertures in a conducting screen. Such a conventional surface is usually planar and formed by etching the array design from a metal clad dielectric substrate. These conventional frequency selective surfaces behave as filters with respect to incident electromagnetic waves with the particular frequency response being dependent on the array element type, the periodicity of the array and on the electrical properties and geometry of the surrounding dielectric and/or magnetic media. The periodicity is the distance between the centres of adjacent elements or between the centres of adjacent apertures.
Such a conventional frequency selective surface has a wide bandwidth and it is desirable to have a surface with a smaller bandwidth which is more selective and which has a relatively large frequency separation between the passband and onset of grating lobes.
There is a need for a generally improved frequency selective surface.